1. Field of the Invention
The present invention relates to a method of forming a water-resistant film on a transparent panel such as a glass panel.
2. Description of the Prior Art
Known processes of forming a water-repellent film on the surface of a glass panel such as an automobile window glass panel or mirror glass panel are disclosed in Japanese laid-open patent publications Nos. 4-338137, 4-359086, 5-24885, and 5-24886, for example.
Specifically, Japanese laid-open patent publication No. 4-338137 shows use of a solution including substituted silicon alkoxide in which part of nonmetal molecules of ceramics composed primarily of SiO.sub.2 is replaced with a fluoroalkyl group, for coating the surface of a glass panel to produce a water-repellent film thereon.
Japanese laid-open patent publication No. 4-359086 shows a coating solution prepared by blending a vehicle containing a metal alkoxide with a certain amount of fluoroalkoxysilane or alkoxysilane.
According to Japanese laid-open patent publication No. 5-24885, a transparent metal film is interposed between the surface of a glass panel and a water-repellent film.
According to Japanese laid-open patent publication No. 5-24886, a film of SiO.sub.2 is formed on the surface of a glass panel, which is then etched to produce surface irregularities, and a water-repellent film is formed on the surface of the glass panel.
Various processes are available for coating the surface of a glass panel with a solution to produce a water-repellent film thereon. They include a dipping process for immersing a glass panel in a coating solution, a spraying process for spraying a coating solution from a spray gun onto a glass panel, a spin-coating process for dropping a coating solution onto a glass panel while the glass panel is being rotated at high speed, thereby to spread the applied coating solution uniformly over the glass panel under centrifugal forces, and a flow process for flowing a coating solution from a nozzle onto an upper edge of a glass panel.
Moldings are bonded to the peripheral edges of automobile window glass panels or the like with an adhesive such as a urethane sealant. A water-repellent film has a poor affinity for such an adhesive. For applying an adhesive to an automobile window glass panel coated with a water-repellent film, it has been customary to apply a masking tape to a peripheral edge of the glass panel, apply a coating solution to the glass panel, thereafter remove the masking tape, and then apply the adhesive to the unmasked edge region.
FIG. 4 of the accompanying drawings is illustrative of such a conventional process of forming a water-repellent film on a glass panel. Specifically, FIG. 4 shows, in fragmentary cross section, a glass panel 100 having a coated region 101 to which a solution is applied to form a water-repellent film 103 and an uncoated edge region 102 from which a masking tape has been peeled off. The water-repellent film 103 has a raised portion 103a which is produced at its edge along the uncoated edge region 102 due to the surface tension of the applied coating solution. FIG. 5 of the accompanying drawings shows the thickness of the water-repellent film 103 as it varies with the distance of the edge of the glass panel 100. The raised portion 103a tends to produce optical interference, making the film edge too conspicuous.